Our research includes the development of high-speed signal processing techniques to implement modems and codecs in highly integrated hardware. We have developed novel complex modulation and demodulation techniques that can be implemented in gate array logic or digital signal processors. We place particular emphasis on synchronous spread spectrum processes and burst acquisition techniques.

Communications Equipment Development
In support of communications testing systems and prototype communication system development, SRI has developed a line of programmable, modular communications elements. Using high-speed, field-programmable gate array and digital signal processing hardware, SRI's transmitter and receiver products can simulate or emulate nearly every kind of communications waveform in use today.

SimCard
SimCard, a general-purpose communication signal generator, was developed in response to the cellular telephone industry's need to emulate CDMA (IS-95) systems. The SimCard can simultaneously generate the four base station signals identified in the IS-95 standard, as well as four reverse link signals, thus emulating multiple mobile transmitters. It can be configured to generate many modulations including binary FSK, m-ary FSK, M-ary Psk, and QAM, and can emulate virtually any data protocol including signal spreading, framing, and scrambling. Although designed for a CDMA system, the SimCard has been embedded in a variety of systems to emulate INMARSAT, Intelsat, and various TDMA signals. The SimCard is currently being marketed by EIP Microwave, Inc.

Cable Modem
In a program for a commercial client, SRI produced a development plan for a head-end cable modem compatible with DAVIC and DVB specifications. We also developed transmitter and receiver cards that implemented protocol specifications for the physical and link layers and part of the network layer. The transmitter card supports bidirectional communication for reservation and contention access; uses channel control filtering and QPSK demodulation; and sends TDM data at 1.544 or 3.088 Mbps and 70-400 MHz (or, optionally, 70-800 MHz). The receiver card implements TDMA access at 1.544 Mbps and 256 kbps; 5-65 MHz receiver channels can be assigned. It supports all physical-layer specifications including burst detection, filtering, QPSK demodulation, descrambling, and R/S decoding; and implements timing measurements and burst power measurements.

Both cards implement an AAL-3 interface for traffic data and support packet formatting, including error control coding, scrambling, and insertion of MAC layer b- and m-bits. The cards are implemented in a single-slot super-Eurocard format. FPGA-based logic signal processing is used in the interface and signal manipulation. This approach makes it easy to incorporate changes and transition to low-cost ASICs. SRI has developed a large library of logic-based communication processes for implementing transmitters and receivers in FPGAs and other logic devices. Our techniques use much lower gate counts than other DSP or discrete process implementations, resulting in greater flexibility and scalability, lower power consumption, and simpler implementations.